This invention is concerned with a new member of the sulfur-containing polypeptide group of antibiotics. This family of antibiotics includes thiostrepton (Antibiotics Ann., 1955-1956, 554-559); siomycin (J. Antibiotics, 14:255, 1961); A-59 (J. Antibiotics, A14:194, 1961); thiopeptin (J. Antibiotics, 23:113-119, 1970); and sporangiomycin (J. Antibiotics, 21:525-531, 1968).